Carbamate plasticizers for natural and synthetic rubber



Patented Dec. 30, 1947 UNITED STATES PATENT OFFICE CARBAMATE PLASTICIZERS FOR NATURAL AND SYNTHETIC RUBBER Arthur W. Campbell, Terre Haute, Ind., assignor to Commercial Solvents Corporation, Terre Haute, Ind., a corporation oi Maryland No Drawing. Application March 13, 1944, Serial No. 526.315

6 Claims. I

wherein R represents a member selected from a group consisting of alkyl and nitroalkyl, R represents a substituent selected from a class consisting of aikyl, aryl, l-ethyli-fl-ethylpentyl)- 3,5-dioxacyclohexyl and tetrahydrofurfuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dialkyl and diaryl, and R and R may also represent a combined group selected from a closs consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

Several plasticizers or softeners have been proposed for natural and various types of synthetic rubber and in certain instances have functioned as such in a relatively efficient manner. Dibutyl phthalate and tricresyl phosphate are among those materials that have previously been used in this capacity. When these compounds exhibit reasonably good softening properties, they are not entirely free from certain material disadvantages such as a comparatively high freezing point and only fair compatibility with the rubber to be plasticized. These defects are obviously of a serious nature since the presence of either tends to bring about premature failure of the rubber article in which the proposed softener as been incorporated.

I hav now discovered a class of compounds, the carbamic acid esters of the types specified above, which exhibit considerably improved plasticizing properties and compatability, as well as a lower freezing point over those materials previously employed as softeners for rubber.

In practicing my invention, the substituted alkylcarbamates can be incorporated in substantially any standard rubber compounding mixtures containing the rubber to be softened. The crude rubber is masticated by passing it through a cold, tight rolling mill several times (5 passes are ordinarily suflicient), pulling the sheet out without folding it each time it passes through the roll. After the rubber has been thoroughly masticated, the other ingredients of the stock 2 are added, the plasticizer being introduced last. Thereafter the stock is thoroughly mixed, the resulting samples placed in an extrusion plastometer of conventional design and the number of seconds required for a given weight of plasticized rubber to be forced from a chamber having an orifice of definite size, under predetermined conditions of temperature and pressure is measured. A suitable design of extrusion plastometer is described in Rubber Chemistry and Technology, vol. 9, pp. 496-501. The apparatus there shown was the type employed in the tests discussed below.

-In addition to serving as plasticizers for natural rubber, the substituted alkyl carbamates of my invention are especially useful as softeners for various classes of synthetic rubber, such as for example, co-polymers of varying percentages of 1,3-butadiene and acrylonitrile; chloroprene polymers; co-polymers of LB-butadiene and styrene, and the like. In general it may be said that these substituted alkyl carbamates function satisfactorily as plasticizers for any synthetic rubber having as a common unit the 1,3-butadiene structure, or a co-polymer of an unsaturated compound having the l,3-butadiene structure and the polymerizable structure As examples of unsaturated monomers capable of being co-poiymerized with a 1,3-butacliene hydrocarbon and having the polymerizable structure last indicated above, there may be mentioned styrene, acrylonitrile, methylacrylonitrile, isobutylene, methyl vinyl ether, vinylidene chloride, methyl l-methylvinyl ketone, and the like. The co-polymerization of compounds containing the 1,3-butadiene skeleton, with unsaturated compounds of the type mentioned immediately above may be accomplished by means of a number of known methods, such as homogeneous polymerization, polymerization in aqueous emulsion, and the like.

The quantity of plasticizer utilized will generally be found to depend upon the particular type of polymer under consideration and the degree of softness desired. While I have found that the plasticizers of my invention are compatible with both natural and synthetic rubber of the general type indicated above, in amounts covering a wide range of proportions, it will ordinarily be observed that such softeners are most advantageously employed in concentrations varying from about 10 to 45 parts by weight for each parts by weight of rubber. Obviously the 3 optimum concentration of plasticizer will vary with the type of rubber to be plasticized.

The substituted alkyl carbamates employed as softeners in my invention may be conveniently synthesized by known methods. A procedure which I have found particularly satisfactory for the synthesis of such compounds involves reacting the desired primary or secondary amine and allwl chloroformate in equimolecular proportions in a suitable solvent such as benzene. Specifically such procedure involves first dissolving the alkyl chloroiormate in the solvent and then adding the amine dropwise while cooling and agitating the reaction mixture. Upon addition of the amine, the corresponding substituted ammonium chloride is observed to separate. This product may be collected on a filter and the benzene contained in the filtrate removed therefrom by distillation under reduced pressure, leaving as a residue the desired substituted alkyl carbamate. Further purification of this product, if a solid, may be effected by recrystallization from benzene, toluene or similar solvents; if it is normally a liquid, purification can be readily eflfected by fractional distillation.

In determining the plasticizing ability of the substituted alkyl carbamates, a mixture having the iollowing composition was employed:

Parts by weight Butadiene-acrylonitrile copolymer 100.0 Zinc oxide 5.0 Stearic acid 1.0 Altax (benzothiazyl disulflde) 1.5 Sulfur 1.5 Channel black 50.0 Plasticizer 30.0

Table I Air Pressure on Diaphragm Compound 5.5 lb., 7.5 lb.,

time,sec. time, sec.

Amyi dibutylearbamata... 4 Butyl diamylcarbamatm i0 3 Amy] diamylcarbamate. l2 3 Hexyl diam ylmrbamate. l2 3 Heryl dibutylcarbamate l6 4 Butyl dibutylcarbamate l7 3 Duty] his(l-methy1hepty1)-mrbamate 1B 5 Buty] diisopropylcarbamate 22 5 Butyl diethylcarbamate z; Butyl butylphenylwbamate 25 7 Butyl tetrahydroiurlurylisopropylcarbamatm. 45 0 Butyl piperidylcarbamate 4o Butyl a-oxapentamethylenemrbamate 46 i8 Ethyl dibutylcarbamate 55 22 Ethyl phenylcarbamata 58 23 Ethyl diphenylmrbamate 78 31 Ethyl but icarbamaie 192 B2 Butyl N- l-ethyl-4-(l-ethylpe yl) 3,5-dioxacyclohexyl] carbamate 23 a Butyl N-z-nitroisobutyl N-isopropylcarbamate 2) l9 2-Nitr0is0butyl N-2-nitro isobutyl Iv-isopro- Bylcarbamatc 32 25 D utyl hthalate 3? l9 Btandar batch, without plasticizer 828 sec 4 A second mixture identical in composition with the one given above. with the exception that another copolymer of 1,3-butadiene and acrylonitrile was substituted for that used previously, was subjected to a series of plasticity tests and the following results were obtained:

Table II Air Pressure on Diaphragm Compound 5.5 lb., .5 lb.. time, sec. time, sec.

Dibutyl lphthalate l2 8 Trims ghosphate l2 9 Butyl ie hylearbamate 0 8 Butyl dibutylcarbamate l0 4 Standard batch, without plasticizer l, 650 201 The ability of the aforesaid carbamates to plasticize natural rubber as well as additional types of synthetic rubber is demonstrated by the data appearing in the table below. In this particular series of experiments butyl dibutylcarbamate was employed as the plasticizer throughout. The stock used was of the same composition as that previously used with the exception that the rubbers indicated were substituted for the previously employed butadiene-acrylonitril polymer.

It is to be strictly understood that the results of the tests in the above tables have been given for the purpose of illustration only and are not to be construed as limiting this invention in any respect. Other plasticizers of the class generally set forth herein may be incorporated in synthetic rubber of various types different from those present in the mixtures utilized in obtaining the data appearing above. Also additional materials such as pigments, fillers, vulcanizing agents, accelerators, anti-oxidants, as well as other softeners or mixtures of softeners of the present invention may be incorporated in the rubber compositions contemplated by my invention. In general, it may be said that any modiflcations or equivalents that would ordinarily occur to those skilled in the art are to be considered as lying within the scope of my invention.

an N-substituted carbamate having the following general formula:

wherein R represents a member selected from a group consisting of alkyl and nitroalkyl, R represents a substituent selected from a class consisting of alkyl, aryl, l-ethy1-4-(l-ethylpentyl)- 3,5-dioxacyclohexyl and tetrahydrofuriuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dialkyl and diary], and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

2. The composition of claim 1 wherein the substituted carbamate is present in a concentration ranging from to 45 per cent by weight based on the weight of the rubber.

3. A composition of matter comprising natural rubber and as a softener therefor an N- substituted carbamate having the following general formula:

wherein R represents a member selected from a group consisting of alkyl and nitroaikyl, R represents a substituent selected from a class consisting of alkyl, aryl, 1-ethyl-4-(1-ethylpentyl)- 3,5-dioxacyclohexyl and tetrahydrofurfuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dialkyl and diary], and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

6 4. A composition of matter comprising a. copoiymer of 1,3-butadiene and acrylonitrile, and as a softener therefor an N-substituted carbamate having the following general formula:

0 RI Hat-M wherein R. represents a member selected from a group consisting of alkyl and nitroalkyl, R represents a substituent selected from a class consisting of alkyl, aryl, 1-ethy1-4-(1-ethy1pentyl)- 3,5-dioxacyclohexyl and tetrahydroiurfuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dlalkyl and diaryl, and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

5. A composition of matter comprising a copolymer of 1,3-butadiene and acrylenitrile, and a suflicient quantity of butyl dibutyl carbamate incorporated therein to soften said copolymer.

6. A composition of matter comprising a copolymer of 1,3butadiene and acrylonitrile, and a sufiicient quantity of amyl dibutyl carbamate incorporated therein to soften said copolymer.

ARTHUR W. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,041,733 Werntz May 26, 1936 2,182,359 Smith Dec. 5, 1939 2,197,479 Meigs Apr. 16, 1940 2,234,204 Starkweather Mar. 11, 1940 2,296,331 Bogemann Sept. 22, 1942 Certificate of Correction Patent N 0. 2,433,595.

ARTHUR w. CAMPBELL December 30, 1947.

It is hereby certified that errors appear in the printed specification of the above numberedpatent requirin class; line 31, for the W011? mixture; and that the said When" read While correction as follows: Column 1, line 22, for close read lines 49 and 50, for mixtures" read Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of April, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner 0/ Patents.

an N-substituted carbamate having the following general formula:

wherein R represents a member selected from a group consisting of alkyl and nitroalkyl, R represents a substituent selected from a class consisting of alkyl, aryl, l-ethy1-4-(l-ethylpentyl)- 3,5-dioxacyclohexyl and tetrahydrofuriuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dialkyl and diary], and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

2. The composition of claim 1 wherein the substituted carbamate is present in a concentration ranging from to 45 per cent by weight based on the weight of the rubber.

3. A composition of matter comprising natural rubber and as a softener therefor an N- substituted carbamate having the following general formula:

wherein R represents a member selected from a group consisting of alkyl and nitroaikyl, R represents a substituent selected from a class consisting of alkyl, aryl, 1-ethyl-4-(1-ethylpentyl)- 3,5-dioxacyclohexyl and tetrahydrofurfuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dialkyl and diary], and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

6 4. A composition of matter comprising a. copoiymer of 1,3-butadiene and acrylonitrile, and as a softener therefor an N-substituted carbamate having the following general formula:

0 RI Hat-M wherein R. represents a member selected from a group consisting of alkyl and nitroalkyl, R represents a substituent selected from a class consisting of alkyl, aryl, 1-ethy1-4-(1-ethy1pentyl)- 3,5-dioxacyclohexyl and tetrahydroiurfuryl, R represents a substituent selected from a class consisting of hydrogen, and nitroalkyl, R and R together may represent substituents selected from a class consisting of dlalkyl and diaryl, and R and R may also represent a combined group selected from a class consisting of polymethylene and oxapolymethylene the terminal carbon atoms of which are bonded to N.

5. A composition of matter comprising a copolymer of 1,3-butadiene and acrylenitrile, and a suflicient quantity of butyl dibutyl carbamate incorporated therein to soften said copolymer.

6. A composition of matter comprising a copolymer of 1,3butadiene and acrylonitrile, and a sufiicient quantity of amyl dibutyl carbamate incorporated therein to soften said copolymer.

ARTHUR W. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,041,733 Werntz May 26, 1936 2,182,359 Smith Dec. 5, 1939 2,197,479 Meigs Apr. 16, 1940 2,234,204 Starkweather Mar. 11, 1940 2,296,331 Bogemann Sept. 22, 1942 Certificate of Correction Patent N 0. 2,433,595.

ARTHUR w. CAMPBELL December 30, 1947.

It is hereby certified that errors appear in the printed specification of the above numberedpatent requirin class; line 31, for the W011? mixture; and that the said When" read While correction as follows: Column 1, line 22, for close read lines 49 and 50, for mixtures" read Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of April, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner 0/ Patents. 

